1. Field of the Invention
This invention relates to high friction surfaces for use in abrasive applications and the preparation of such high friction surfaces. In particular, the present invention relates to abrasive tools prepared by use of a matrix of braze paste and abrasive particles which have been prepared on a fixture.
2. Description of the Prior Art
U.S. Pat. No. 3,913,217, hereinafter referred to as Oliver I, discloses an abrasive tool comprising a tool blank having small steel balls secured thereto which have been armed with magnetically oriented carbide particles. The carbide particles are secured together and to the balls by a braze alloy. An Oliver I type tool is typically prepared, in part, by first securing a single layer of small steel balls to the surface of a tool blank. A magnet is then secured to the tool blank below the balls. Next, magnetizable carbide particles are sprinkled onto the small steel balls. The magnetic flux concentrations produced by the flux path passing through the small steel balls cause carbide particles to collect on the outermost portions of the balls to form conical structures. A braze paste consisting of a binder and a braze alloy is then applied to encapsulate all of the elements of the assembly. Finally, the entire assembly is subjected to heating in a brazing furnace which bonds the braze alloy, the magnetizable particles and the balls into a unified structure. When the assembly has cooled, it may be used as an abrasive tool.
Thus, Oliver I discloses an IN-SITU technique for preparing an abrasive tool which requires placement of permanent tool protrusions on the external surface of a tool blank. These tool protrusions are the necessary surface for the magnetic formation of the conical structures of particles on the tool. The protrusions may take the form of small steel balls (as described in the '217 patent) or shapes formed by machining a profile in the external surface of the tool blank. In either case, the tool blank which is the foundation of the ultimate product must be covered with protrusions. The small steel balls or other protrusions formation are an added material cost and require additional labor to apply. If the protrusions are produced by machining a profile in the external surface of the tool blank, substantial skill and specialized equipment must be used.
Further, the carbide particles form structures which align with the magnetic flux emanating from the magnetized tool blank. In the case of a cylindrical structure, the cones align with magnetic flux emanating radially from the circumferential portion of the wheel. The conical structures formed thereby will be symmetrical in all respects, and when used as a cutting tool will offer a negative rake angle to the workpiece. The Oliver I technique is capable of producing only these symmetrical conical structures. If more aggressive rake angles or selectively oriented conical structures are desired, the Oliver I technique is not appropriate.
Finally, as with any cutting or abrading tool, heat produced during cutting and abrading is conducted from the point of contact between the tool and the workpiece into the structure of the tool. When using an Oliver I type tool, heat passes from the conical structures through small steel balls and into the tool blank. Since these balls are brazed to the tool blank, they offer little more than point contact and consequently present a substantial impediment to the flow of heat.
U.S. Pat. No. 4,916,869 hereinafter referred to as Oliver II, also discloses an abrasive grit structure comprising a plurality of peaked portions. However in Oliver II each peak has an apex including an abrasive grit particle which is surrounded by setting material that forms a substrate layer on which the peak portions are secured to provide an integral structure. In a first embodiment, the peaked portions are formed by using a mold having a plurality of concave indentations each of which receives an abrasive grit particle that is then surrounded by setting material to establish an integral structure. The setting material may contain additional abrasive particles. A second embodiment discloses a technique for molding using a mold having a plurality of concave indentations which are filled with abrasive grit particles that are then transposed to a substrate surface as individual abrasive elements. Such a concept and structure is similarly described in Woodell, et al. U.S. Pat. Nos. 2,001,911, Marvin 2,793,427, Heck 3,431,105 and Bellinger 3,102,011. In a third embodiment, a monolayer of abrasive particles are distributed on a flat planar surface and structurally interconnected by a first layer of resin saturated braze alloy and a second layer of resin saturated setting material. In the first and second embodiment, a braze alloy paste is applied to the abrasive grit structure after the structure has been applied to a tool surface (i.e., IN-SITU). In the third embodiment the braze alloy may be applied before the abrasive structures are applied to the ultimate tool (NON IN-SITU). Upon heating to braze conditions, the braze alloy infiltrates the abrasive grit structure and bonds the abrasive particles and setting materials to the tool surface.